The present invention relates to a knocking control system and method for a multi-cylinder internal combustion engine and more particularly to a system and a method for suppressing engine knocking in each of the engine cylinders of a vehicular engine.
It is important to determine the ignition timing of the internal combustion engine so as to produce the best efficiency for current conditions. In general, ignition timing most preferably approaches MBT (Minimum Advance for Best Torque) as long as engine knocking does not occur.
A Japanese Patent Application Unexamined Open No. Sho 59-196973 published on Nov. 8, 1984 exemplifies a conventional knocking control system. In the above-identified Japanese document, the ignition timing for each of the engine cylinders is retarded when knocking occurs in the corresponding engine cylinder. In this way, knocking is controlled by controlling the engine ignition timing separately for each cylinder.
However, in this conventional knocking control system, the retardation angle correction amount applied to the ignition timing of each cylinder is independent of the other retardation angle correction amounts for the other engine cylinders. Therefore, if a knock detection system for a particular engine cylinder malfunctions, the ignition timing of that engine cylinder may be advanced to the extreme so that the knocking in that engine cylinder becomes very intense. Consequently, the durability of the engine is reduced.
On the other hand, another knocking control system has been developed which has a fail-safe system capable of coping with malfunction of the knock detection system in each cylinder. This is exemplified by a Japanese Patent Application Examined Open No. Sho 60-20584.
In the above-identified Japanese document, in cases where knocking information is not available due to malfunction of the knock detection system and therefore correction of the retardation angle is not possible, malfunction of the vibration acceleration detection system used to detect engine knocking is detected and a retardation angle correction of the ignition timing is carried out. As a result, unnecessary correction of the retardation angle is prevented and the safety of the engine is taken into consideration when malfunction of the knock detection system is detected.
However, the above-described knocking control system does not detect knocking in each engine cylinder but merely performs blanket control of all of the engine cylinders. In addition, at low engine speeds at which the background vibration level of the engine is reduced, the difference between the knocking sensor output signal levels during malfunction of the knocking sensor and during normal operation thereof is not conspicuous, and therefore, difficulties arise in detecting malfunction of the knock detection system.
Hence, the above-described knocking control system does not solve the above-described problem of the conventional knocking control system for the individual engine cylinders.